The use of <scp>L</scp>-DOPA to enhance visualization of the 'black line' between species of the Armillaria mellea complex

The zone of antagonism, known as the &quot;black line,&quot; that occurred between the confronting margins of diploid isolates of different Armillaria mellea complex species was enhanced by incubation in L-β-3,4-dihydroxyphenylalanine (L-DOPA). Intraspecific crosses and crosses of genetically identical isolates did not produce a black line after similar treatment with L-DOPA.